The present invention relates generally to the initial synchronization methods and more specifically to an improvement in the steps of the initial synchronization methods.
Although the method will be described for mobile WiMAX systems (IEEE 802.16e, WiBro) as an example, it is applicable to other communication systems and protocols. The initial synchronization methods generally include a frame boundary search, fractional/integer frequency offset estimation, and segment/cell ID searches.
The present method of initial synchronization of a communication signal includes the steps of symbol boundary search, fractional frequency offset estimation, fractional frequency offset compensation, frame boundary search, integer frequency offset estimation, integer frequency offset compensation, preamble segment ID search and preamble cell ID search.
The symbol boundary search includes estimating the boundary of a present data symbol by a correlation index for the present data symbol and the correlation index for the next data symbol. The combined correlation index is
      i    ^    =                    arg        ⁢                                  ⁢        max            i        ⁢                                  ∑                      v            =            0                                G            -            1                          ⁢                  {                                                    y                                  i                  +                  v                                            ⁢                              y                                  i                  +                  v                  +                                      N                    FFT                                                  *                                      +                                          y                                  i                  +                  v                  +                  G                  +                                      N                    FFT                                                              ⁢                              y                                  i                  +                  v                  +                  G                  +                                      2                    ⁢                                          N                                              FFT                        )                                                                                            *                                              }                          where i denotes the correlation index, G the cyclic prefix length, y the observed time domain samples, and NFFT the size of the symbol. The combined correlation index i is calculated iteratively as follows:
                    i        ^            =                                    arg            ⁢                                                  ⁢            max                    i                ⁢                                        C            ⁡                          (              i              )                                                      ,                  ⁢                  where        ⁢                                  ⁢                  C          ⁡                      (            0            )                              =                        ∑                      v            =            0                                G            -            1                          ⁢                              {                                                            y                  v                                ⁢                                  y                                      v                    +                                          N                      FFT                                                        *                                            +                                                y                                      v                    +                    G                    +                                          N                      FFT                                                                      ⁢                                  y                                      v                    +                    G                    +                                          2                      ⁢                                              N                                                  FFT                          )                                                                                                      *                                                      }                    ⁢                                          ⁢          and                                C      ⁡              (                  i          +          1                )              =                  C        ⁡                  (          i          )                    +              (                              y                          i              +              G                                ⁢                      y                          i              +              G              +                              N                FFT                                      *                          )            +              (                              y                          i              +                              2                ⁢                G                            +                              N                FFT                                              ⁢                      y                          i              +                              2                ⁢                G                            +                              2                ⁢                                  N                  FFT                                                      *                          )            -              (                              y            i                    ⁢                      y                          i              +                              N                FFT                                      *                          )            -              (                              y                          i              +              G              +                              N                FFT                                              ⁢                      y                          i              +              G              +                              2                ⁢                                  N                  FFT                                                      *                          )            
The frame boundary search includes identifying the preamble symbol in the symbols found in the symbol boundary search to determine the frame boundary. Identifying the preamble symbol includes grouping the subcarriers into K subgroups of N consecutive subcarriers, where K is the number of subcarriers that define a specific segment group of subcarriers; collecting the distributed energies on subcarriers; and making a decision if the current symbol is preamble based on a threshold that is estimated by stochastic count process model.
The integer frequency offset is estimated from the pilot subcarriers of the frame control header of the frame without decoding the down load MAP.
The preamble segment ID search is based on:
      n    ^    =                    arg        ⁢                                  ⁢        max                    n        ⁢                                  ⁢        ε        ⁢                  {                      0            ,            1            ,            2                    }                      ⁢          {                        ∑                      k            =            0                                K            -            1                          ⁢                                                      y              FFT                        ⁡                          (                              PreambleCarrierSet                n                k                            )                                                    }      where PremableCarrierSetnk=n+N·k, the group index of N groups n=0, 1, 2 . . . N−1, and the subcarrier index of a K length PN sequence k={0, 1, 2 . . . K−1}.
The preamble cell ID search includes estimating the symbol timing offset {circumflex over (ε)}|nr by:
            ɛ      ^              ❘      n        r    =      arg    ⁢          {                                    N            FFT                                2            ⁢            π            ⁢                                                                          m                                      k                    +                    1                                                  -                                  m                  k                                                                                  ⁢                                         [                                          ∑                                                      m                    k                                    ,                                                            m                                              k                        -                        1                                                              ⁢                    ε                    ⁢                                          {                                              non                        ⁢                                                  -                                                ⁢                        zero                        ⁢                                                                                                  ⁢                        subcarrier                                            }                                                                                                                                    ⁢                                                (                                                                                    y                        FFT                                            ⁡                                              (                                                  m                                                      k                            ⁢                                                                                                                  +                            1                                                                          )                                                              ×                                          sign                      ⁡                                              (                                                  pilot                                                      m                                                          k                              +                              1                                                                                                            r                            ,                            n                                                                          )                                                                              )                                ×                                                      (                                                                                            y                          FFT                          ′                                                ⁡                                                  (                                                      m                            k                                                    )                                                                    ×                                              sign                        ⁡                                                  (                                                      pilot                                                          m                                                              k                                ⁢                                                                                                                                  ⁢                                1                                                                                                                    r                              ,                              n                                                                                )                                                                                      )                                    *                                                      ]                    }                    where the group index of N groups n=0, 1, 2 . . . N−1, cell ID of R cell IDs in a segment group rε{0, 1, . . . , R−1}, mk and mk+1 are two neighboring subcarrier positions, the subcarrier index of a K length PN sequence k={0, 1, 2 . . . K−1} and pilotmr,n represents the modulated PN sample for the preamble.
The preamble cell ID is estimated by:
      r    ^    =                    arg        ⁢                                  ⁢        max            r        ⁢          {                                                            ∑                              m                ∈                                  {                                      non                    ⁢                                          -                                        ⁢                    zero                    ⁢                                                                                  ⁢                    subcarrier                                    }                                                                                                  ⁢                                          real                ⁡                                  (                                      z                    m                    r                                    )                                            ×                              sign                ⁡                                  (                                      pilot                    m                                                                  n                        ^                                            ,                      r                                                        )                                                                              2            }      where
            z      m      r        =                            y          FFT          ′                ⁡                  (          m          )                    ×              exp        ⁡                  (                      j2π            ⁢                                                  ⁢                          m                              N                FFT                                      ⁢                                          ɛ                ^                                            ❘                n                            r                                )                      ,mε{non-zero subcarriers}, NFTT is the symbol size.
These and other aspects of the present invention will become apparent from the following detailed description of the invention, when considered in conjunction with accompanying drawings.